In short-range traffic, the performance of propeller-driven aircraft is basically always superior to jet-driven aircraft performance. Propeller-driven aircraft engines have shorter start-up requirements. They consume less fuel and in case of the short-range traffic mentioned above, they also have lower maintenance requirements than jet-driven aircraft. This means considerably lower maintenance costs on the whole.
Engine mounts of propeller-driven aircraft are, however, exposed to distinct interfering excitation which, in their entirety, result in a transmission of vibration to the supporting structure to which the respective engine mount is mounted. The vibrations extending via the supporting structure result in a considerable reduction of travelling comfort in propeller-driven aircraft. There is such a great difference in travelling comfort between propeller-driven and jet-driven aircraft that jet-driven aircraft is often actually used for short-range traffic in order to keep passengers and in order to prevent their availing themselves of the services of other airlines.
An engine mount as described at the beginning is known from DO 328 Regional Airliner, a propeller-driven aircraft manufactured by Dornier Luftfahrt GmbH, Germany. The engine is bolted to one end of the tubular frame structure by means of so-called shock mounts. The respective end of the tubular frame structure is made up of a so-called horse collar. The horse collar is connected with a U-shaped, vertically-arranged center frame, which is open at the base, by means of V-shape arranged members of the tubular frame structure. This center frame, in turn, is connected with a vertical frame made up of members of the tubular frame structure by members of the tubular frame structure arranged in a V-shape. At the top, this vertical frame is rigidly mounted to a cowling box. Further members of the tubular frame structure extend from the vertical frame backwards, and converge in a junction point, for which a mount. is provided at the cowling box for the absorption of vertical forces. Besides the engine being bolted to mounts at the horse collar, the engine is suspended at the center frame, this suspension tolerating the engine's thermal expansion towards the tubular frame structure. The shock mounts by means of which the engine is mounted to the horse collar are made up of elastomer materials and are to isolate the engine's vibrations from the tubular frame structure due to their deforming properties. The shock mounts must, however, not only be optimized with a view to their vibration-isolation properties. Their mechanical and thermal strains in engine operation must primarily be taken into account. Additional factors to be considered are the spontaneous increase in hardness during the shock mounts' service life as a consequence of these mechanical and thermal strains as well as external influences such as the weather, salt used for runway de-icing purposes and engine oil. All of these factors result in the shock mounts being subjected to an artificial aging process. The shock mounts' vibration isolation capacity is therefore insufficient even if shock mounts are replaced every 6,000 flying hours, as requested.
The invention not only refers to engine mounts for the attachment of an engine to a cowling box. In particular with a view to one-engine propeller-driven aircraft, the fuselage or its frame shall also be considered as a supporting structure for the engine. Engine mounts according to the invention are also suitable for jet-driven engines even if the problems mentioned above primarily occur in propeller-driven engines.
The invention is based on the task of providing an engine mount as described at the beginning which is particularly suitable for the purpose of active vibration isolation and which, at the same time, has a sufficient degree of passive stability (fail-safe) and is light-weight.